The present invention relates generally to sectorized cellular communication systems and, more particularly, to antennas for use in such systems.
Pyramidal horns having corrugated interior surfaces have been known for use in microwave systems for many years.
Sectorized cellular communication systems have also been known for many years, and are in widespread commercial use. Sectorized cellular systems typically use directional antennas to separate signals radiated at similar frequencies. In theory, the antenna for each sector has a specified azimuthal beamwidth to reduce interference from both customer equipment and cell-site equipment in other cells. However, interference can increase if the antennas serving the sectors do not produce azimuth-plane patterns that drop off sharply at the edges of their respective sectors, and patterns that do not have large sidelobes and backlobes. Producing such patterns becomes more challenging as the number of sectors in a cell is increased and the sector sizes become smaller, e.g., from three 120xc2x0 sectors to nine 40xc2x0 sectors, or to twelve 30xc2x0 sectors.
In accordance with the present invention, there is provided an antenna for use in a sectorized cellular communication system, the antenna comprising a wide-flare pyramidal horn having two pairs of opposed flared side walls, at least one of the two pairs of opposed walls having corrugated interior surfaces, the length of the horn and the flare angle of the walls having the corrugated interior surfaces being selected to produce a ratio xcex94e/xcex greater than 1.5, where
xcex94e=[a/2/xcex] tan (xcex1e/2) is the spherical-wave error of said horn, xcex is the free space wavelength of the microwave signals to be transmitted by said antenna, a is the aperture width and xcex1e is the horizontal half-angle of the horn.
The azimuthal pattern has a half-power beam width that is substantially as wide as the azimuthal width of the specified sector and drops sharply at both azimuthal edges of that sector. In the elevation plane, The elevation pattern is substantially free of nulls across a specified elevation-plane beam width (typically xc2x125xc2x0).
When used in a sectorized cellular communication system, this antenna is capable of producing specified patterns in both the azimuth and elevation planes of a specified azimuthal sector with a specified ground range within a cell.